Answer
These subhsells have the same number of electrons.
Work Step by Step
The $d$ subshell can hold up to 10 electrons. If the $d$ subshell is closed, then it holds 10 electrons.
If the $3d$ subshell is closed, then it holds 10 electrons.
If the $4d$ subshell is closed, then it holds 10 electrons.
These subhsells have the same number of electrons.